The present invention relates to the field of switches for electric motors and, more particularly, to a switch and casing arrangement whereby travel of the switch is limited to moving only one position at a time.
Electric motors have enjoyed widespread use in a variety of devices, particularly since their small size facilitates employment in hand-held devices. Electric drills, hot air dryers, and mixers are but a few of the different types of tools which employ electric motors. An example of such a device is the portable, electric drill which is the subject of U.S. Pat. No. 4,348,603 to Huber.
The motor in such a device typically comprises a fixed field assembly provided with one or more field windings which produce, upon energization, a magnetic field for effecting rotational movement of an armature positioned within the field assembly. Examples of such motors and, in particular, the field assembly therefor may be found in U.S. Pat. No. 3,979,615 to Neff, U.S. Pat. No. 4,038,573 to Hillyer et al, and U.S. Pat. No. 4,071,793 to Cox.
Such motors further include a commutator section having multiple windings or coils affixed to one end of the armature and disposed to coact with a plurality of brushes. As the armature turns, the commutator moves with it and contact is alternately made and broken with the brushes, resulting in reversing the magnetic field of the armature coils connected to the commutater bars in contact with the brushes. This produces the desired rotational movement in a well-known fashion. An example of such of motor in which the brushes are disposed on a sub-assembly surrounding the commutator can be found in U.S. Pat. No. 4,056,749 to Carlson, Jr. et al.
It is further known in the art to change the direction of current flow through either the field windings or armature windings, with respect to each other, in order to effect reversal of the direction of rotation of the armature. This is desirable, for example, in the case of an electric drill so as to engage and then disengage the drill bit from the material being worked upon. Examples of switches designed for accomplishing such reversal of current may be found in U.S. Pat. No. 3,398,250 to Bowers, U.S. Pat. No. 3,959,756 to Deming and U.S. Pat. No. 3,691,322 to Matthews.
Since motorized devices, whether designed for consumer or industrial use, are typically mass-produced, it is desirable to provide means for constructing the devices at a low cost. This raises considerations such as use of a minimum number of components, ease of assembly, and reliability in the field during actual usage. Thus, although the prior art is replete with examples of motorized tools and related sub-assemblies, there constantly exists a need for improving the construction of such devices so as to achieve reduced manufacturing costs and increased operating reliability.
For example, prior art techniques of assembling such tools involve axially sliding the brush-bearing sub-assembly over the commutator and into contact with the field assembly. Thereafter, a current reversing switch is typically provided as an element separate from said sub-assembly. However, the need for two separate elements, as well as the necessity of having to slide one part over another rather than simply fitting each into place in a single action, makes for a more difficult assembly operation. This difficult operation frequently requires that the tool, or portions thereof, be assembled by hand rather than by an automated process.